Rotorcraft having a rotary wing and at least two propellers, and a method applied by the rotorcraft

Abstract

A rotorcraft comprising a fuselage, a single main rotor, and a first propeller and a second propeller. The rotorcraft has an adjustment system configured, at least during a stage of hovering flight, to position the first propeller in a first low speed configuration in order to exert a first thrust including a first horizontal component and a first vertical component, the adjustment system being configured, at least during the stage of hovering flight, to position the second propeller in a second low speed configuration so as to exert a second thrust comprising a second horizontal component and a second vertical component.

What is claimed is: 
     
       1. A rotorcraft comprising a fuselage, the fuselage extending longitudinally from rear to front from a tail to a nose, and transversely from a first flank to a second flank, the fuselage extending vertically upwards and surmounted by a single main rotor contributing to providing the rotorcraft with at least part of the lift of the rotorcraft, the rotorcraft having a rectangular reference frame presenting a first unit vector extending in a forward direction from a center of gravity of the rotorcraft towards the front, the rectangular reference frame presenting a second unit vector extending from the center of gravity in a direction going from the first flank to the second flank, and the rectangular reference frame presenting a third unit vector extending in an elevation direction from the center of gravity towards the main rotor, the rotorcraft comprising a first propeller and a second propeller carried respectively by two arms and capable of exerting respectively first thrust and second thrust, the two arms not forming a canard wing, the first propeller and the second propeller arranged transversely on either side of the fuselage, the first propeller and the second propeller respectively having first blades and second blades for rotating respectively about a first axis of rotation and a second axis of rotation, the first blades presenting pitch capable of varying collectively uniformly over a first pitch range generating the first thrust directed towards the front of the rotorcraft and over a second pitch range generating the first thrust directed towards the rear of the rotorcraft,
 wherein the rotorcraft includes an adjustment system acting on the first propeller and the second propeller, the second blades presenting pitch capable of varying collectively uniformly at least over a third pitch range generating the second thrust directed solely towards the front of the rotorcraft, the adjustment system configured, at least during a stage of hovering flight, to position the first propeller in a first low speed configuration, the first thrust in the first low speed configuration having a first horizontal component directed parallel to the first vector and in a direction opposite to the first vector, and a first vertical component directed parallel to the third vector in the elevation direction, the adjustment system configured, at least during the stage of hovering flight, to position the second propeller in a second low speed configuration, the second thrust in the second low speed configuration comprising a second horizontal component directed parallel to the first vector and in the same direction as the first vector, and a second vertical component directed parallel to the third vector in the same direction as the third vector. 
 
     
     
       2. The rotorcraft according to  claim 1 , wherein the adjustment system is configured to position the first propeller in the first low speed configuration and the second propeller in the second low speed configuration when the rotorcraft is traveling forwards at a speed less than a speed threshold. 
     
     
       3. The rotorcraft according to  claim 1 , wherein in the first low speed configuration the first thrust presents an acute angle of less than 90 degrees relative to a horizontal plane containing the first vector and the second vector, the second thrust presenting an acute angle of less than 90 degrees with that horizontal plane. 
     
     
       4. The rotorcraft according to  claim 1 , wherein the adjustment system is configured to position the first propeller in a first high speed configuration and the second propeller in a second high speed configuration when the rotorcraft is flying forwards at a speed greater than or equal to a speed threshold, the first thrust in the first high speed configuration having a first horizontal component directed parallel to the first vector and in the same direction as the first vector, and a first vertical component directed parallel to the third vector in a direction opposite to the direction of the third vector, the second high speed configuration is identical to the second low speed configuration. 
     
     
       5. The rotorcraft according to  claim 1 , wherein when the rotorcraft is flying forwards at a speed greater than or equal to a speed threshold, and when seen in a transverse direction going from the first propeller towards the second propeller, the first thrust presents a first acute angle relative to a horizontal plane containing the first vector and the second vector, the second thrust presenting a second acute angle opposite to the first acute angle relative to the horizontal plane. 
     
     
       6. The rotorcraft according to  claim 1 , wherein, when seen in a transverse direction going from the first propeller towards the second propeller, the first axis of rotation presents a first acute angle with a horizontal plane containing the first vector and the second vector, the second axis of rotation presenting a second acute angle opposite to the first acute angle relative to the horizontal plane. 
     
     
       7. The rotorcraft according to  claim 1 , wherein the first propeller and the second propeller present fixed settings, the first axis of rotation and the second axis of rotation are fixed relative to the fuselage. 
     
     
       8. The rotorcraft according to  claim 7 , wherein the first propeller comprises a first propeller shaft for rotating a first hub carrying first blades, the second propeller comprises a second propeller shaft for rotating a second hub carrying second blades, and the adjustment system comprises a first device fastening the first propeller shaft to one of the arm while imparting to the first propeller shaft a single degree of freedom to move in rotation about the first axis of rotation relative to the fuselage, the adjustment system comprising a second device fastening the second propeller shaft to the other arm while conferring to the second propeller shaft a single degree of freedom to move in rotation about the second axis of rotation relative to the fuselage. 
     
     
       9. The rotorcraft according to  claim 1 , wherein the adjustment system is configured to position the first propeller in a first high speed configuration and the second propeller in a second high speed configuration when the rotorcraft is flying forwards at a speed greater than or equal to a speed threshold, the first thrust in the first high speed configuration comprising solely a first horizontal component directed parallel to the first vector and in the same direction as the first vector, the second thrust in the second high speed configuration comprising solely a second horizontal component directed parallel to the first vector and in the same direction as the first vector. 
     
     
       10. The rotorcraft according to  claim 1 , wherein when the rotorcraft is flying forwards at a speed greater than or equal to a speed threshold, the first thrust and the second thrust are coplanar, the first thrust and the second thrust are parallel to a horizontal plane containing the first vector and the second vector. 
     
     
       11. The rotorcraft according to  claim 1 , wherein the first propeller comprises a first propeller shaft for rotating a first hub carrying blades, the second propeller comprises a second propeller shaft for rotating a second hub carrying blades, and the adjustment system comprises a first mobility system configured to move the first propeller shaft in rotation about a tilt axis imparting to the first propeller shaft relative to the fuselage solely one degree of freedom to move in rotation about the first axis of rotation and one degree of freedom to move in rotation about the tilt axis, the adjustment system including a second mobility system configured to move the second propeller shaft in rotation about the tilt axis imparting to the second propeller shaft relative to the fuselage solely one degree of freedom to move in rotation about the second axis of rotation, and one degree of freedom to move in rotation about the tilt axis. 
     
     
       12. The rotorcraft according to  claim 11 , wherein the first propeller is configured to tilt in a first tilt direction from a first position held in the first low speed configuration to a second position held in the first high speed configuration, the first axis of rotation and the first thrust coinciding and presenting a first acute angle of less than 90 degrees relative to a horizontal plane containing the first vector and the second vector in the first position, the first axis of rotation and the first thrust are parallel to the horizontal plane in the second position; and
 wherein the second propeller is configured to tilt in a second tilt direction from a third position held in the second low speed configuration to a fourth position held in the second high speed configuration, the second axis of rotation and the second thrust coinciding and presenting a second acute angle of less than 90 degrees relative to the horizontal plane, the second tilt direction is opposite to the first tilt direction when seen in a transverse direction going from the first propeller to the second propeller, the second axis of rotation and the second thrust are parallel to the horizontal plane in the fourth position. 
 
     
     
       13. The rotorcraft according to  claim 11 , wherein the main rotor includes main blades rotating about a main axis of rotation of the main rotor, the tilt axis intersecting the main axis of rotation. 
     
     
       14. The rotorcraft according to  claim 12 , wherein the first propeller presents a first thrust center positioned on the tilt axis and the second propeller presents a second center of thrust positioned on the tilt axis. 
     
     
       15. The rotorcraft according to  claim 9 , wherein the first propeller comprises a first propeller shaft for rotating a first hub carrying first blades, the second propeller comprises a second propeller shaft for rotating a second hub carrying second blades, and the adjustment system includes a first device for cyclically modifying the pitch of the blades of the first propeller and a second device for cyclically modifying the pitch of the blades of the second propeller. 
     
     
       16. A method of optimizing the lift of the rotorcraft according to  claim 1 , in which the method includes the following step:
 positioning the first propeller in the first low speed configuration and the second propeller in the second low speed configuration during a stage of hovering flight. 
 
     
     
       17. The method according to  claim 16 , wherein the method includes the following step:
 positioning the first propeller in the first high speed configuration and the second propeller in the second speed configuration when the rotorcraft is traveling forwards at a speed greater than or equal to a speed threshold. 
 
     
     
       18. A rotorcraft comprising a fuselage extending vertically upwards and surmounted by a main lift rotor, the rotorcraft having a rectangular reference frame presenting a first unit vector extending in a forward direction from a center of gravity of the rotorcraft towards the front, the rectangular reference frame presenting a second unit vector extending from the center of gravity in a direction going from the first flank to the second flank, and the rectangular reference frame presenting a third unit vector extending in an elevation direction from the center of gravity towards the main lift rotor, the rotorcraft comprising a first propeller and a second propeller carried respectively by two arms and capable of exerting respectively first thrust and second thrust, the first propeller and the second propeller arranged on opposite sides of the fuselage, the first propeller and the second propeller respectively having first blades and second blades rotatable respectively about a first axis of rotation and a second axis of rotation, the first blades presenting pitch capable of varying over a first pitch range generating the first thrust directed towards the front of the rotorcraft and over a second pitch range generating the first thrust directed towards the rear of the rotorcraft,
 wherein the rotorcraft includes an adjustment system for acting on the first propeller and the second propeller, the second blades presenting pitch capable of varying over a third pitch range generating the second thrust directed towards the front of the rotorcraft, the adjustment system configured, at least during a stage of hovering flight, to position the first propeller in a first low speed configuration, the first thrust when the first propeller is in the first low speed configuration having a first horizontal component directed parallel to the first vector and in a direction opposite to the first vector, and a first vertical component directed parallel to the third vector in the elevation direction, the adjustment system configured, at least during the stage of hovering flight, to position the second propeller in a second low speed configuration, the second thrust when the second propeller is in the second low speed configuration comprising a second horizontal component directed parallel to the first vector and in the same direction as the first vector, and a second vertical component directed parallel to the third vector in the same direction as the third vector. 
 
     
     
       19. The rotorcraft according to  claim 1 , wherein the adjustment system is configured to position the first propeller in the first low speed configuration and the second propeller in the second low speed configuration when the rotorcraft is traveling forwards at a speed less than a speed threshold, and wherein when the first propeller is in the first low speed configuration the first thrust presents an acute angle of less than 90 degrees relative to a horizontal plane containing the first vector and the second vector, the second thrust presenting an acute angle of less than 90 degrees with that horizontal plane. 
     
     
       20. The rotorcraft according to  claim 18 , wherein the first propeller comprises a first propeller shaft for rotating a first hub carrying first blades, the second propeller comprises a second propeller shaft for rotating a second hub carrying second blades, and the adjustment system includes a first device for cyclically modifying the pitch of the blades of the first propeller and a second device for cyclically modifying the pitch of the blades of the second propeller.